linux-kernel - Re: [PATCH] drivers/core/of: Add symlink to device-tree from devices with an OF node

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Message-ID: <CAL_Jsq+YyfMWxiOFv4x3g5hZJH0XRqCKj2He1XO9eyXWjHTMrg@mail.gmail.com>
Date:	Tue, 18 Nov 2014 10:37:08 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Jeremy Kerr <jeremy.kerr@....ibm.com>
Subject: Re: [PATCH] drivers/core/of: Add symlink to device-tree from devices
 with an OF node

On Wed, Nov 12, 2014 at 7:10 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
> So I've been annoyed lately with having a bunch of devices such as i2c
> eeproms (for use by VPDs, server world !) and other bits and pieces that
> I want to be able to identify from userspace, and possibly provide
> additional data about from FW.
>
> Basically, it boils down to correlating the sysfs device with the OF
> tree device node, so that user space can use device-tree info such as
> additional "location" or "label" (or whatever else we can come up with)
> propreties to identify a given device, or get some attributes of use
> about it, etc...
>
> Now, so far, we've done that in some subsystem in a fairly ad-hoc basis
> using "devspec" properties. For example, PCI creates them if it can
> correlate the probed device with a DT node. Some powerpc specific busses
> do that too.
>
> However, i2c doesn't and it would be nice to have something more generic
> since technically any device can have a corresponding device tree node.
>
> This patch adds an "of_node" symlink to devices that have a non-NULL
> dev->of_node pointer, the patch is pretty trivial and seems to work just
> fine for me.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 20da3ad..8c7b607 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -493,6 +493,15 @@ static int device_add_attrs(struct device *dev)
>                         goto err_remove_dev_groups;
>         }
>
> +#ifdef CONFIG_OF
> +       if (dev->of_node) {

if (IS_ENABLED(CONFIG_OF) && dev->of_node)

> +               error = sysfs_create_link(&dev->kobj, &dev->of_node->kobj,
> +                                         "of_node");
> +               if (error)
> +                       dev_warn(dev, "Error %d creating of_node link\n", error);
> +       }
> +#endif /* CONFIG_OF */
> +
>         return 0;
>
>   err_remove_dev_groups:
>
>
--
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